Tractor shovel boom raising and lowering means



Aug. 5, 1958 R. L. BEYERSTEDT TRACTOR SHOVEL BOOM RAISING AND LOWEIRING MEANS Filed June 8, 1956 2 Sheets-Sheet 1 L B INVENTZZdZ 9am B Aug. 5, 1958 R. L. BEYERSTEDT TRACTOR SHOVELBOOM RAISING AND LOWERING MEANS 7 Filed June 8, 1956 2 Sheets-Sheet 2 Fig.3

United States Patent Ofiice 2,846,097 Patented Aug. 5, 1958 TRACTOR SHOVEL BOOM RAISING AND LOWERING MEANS Ralph L. Beyerstedt, Libertyville, Ill., assiguor to The Frank G. Hough Co., a corporation of Illinois Application June 8, 1956, Serial No. 590,276

8 Claims. (Cl. 214-140) This invention relates generally to material handling equipment, and more specifically to an improved boom construction for a front end type power loader.

Front end type power loaders as generally known in the art comprise a tractor or prime mover having a digging implement such as a bucket operatively mounted to extend from the front end thereof. The bucket, which is controlled by an operator from an operators station on the tractor, is carried by a boom which is pivotally mounted to the tractor. Some linkage means also mounted between the tractor and the bucket permit the bucket to be positioned in any number of difierent positions relative to the boom. Hydraulic rams and the controls therefor are usually used to raise and lower the boom and operate the linkage means.

In the design and use of these loaders many problems arise when the various parts such as the hydraulic ram means and the boom and linkage means are fabricated and mounted on the tractor. For example, the loader should be designed so that the boom can be etficiently raised and lowered considering, the need for safety to the operator, the necessary requirements for the movement of the bucket relative to any material being dug or to any hopper or truck in which the material is dumped, the need for an efiicient distribution of the combined load of the boom, the bucket and any load within the bucket so that undesirable stresses are not produced and so that proper traction is available at the ground-engaging elements or wheels of the tractor, and the necessary requirements for efliciently using the hydraulic means available for operating the tool means of the loader. Generally in the art these various needs are compromised with the result that some of the possible efliciencies and economies in the fabrication and operation of the various parts are sacrificed.

It is the object of the present invention to provide a loader construction wherein a highly efficient fabrication and operation of the various parts result.

It is a further object of the present invention to provide a novel boom and hydraulic ram means construction wherein many of the existing problems in the art are efiiciently and economically solved.

It is another object of the present invention to provide a boom and hydraulic ram means construction wherein the construction is such that no portion of the boom will obstruct or interfere with an operator within the operators compartment, wherein the construction is such that the bucket is at all times operatively carried closely adjacent to the front end of the tractor, and wherein the construction is such that the boom may be raised to a high lift dump position while avoiding the linkage means connected to the tractor at a point forwardly and below the pivotal connection of the boom on the tractor.

It is another object of the present invention to provide a novel boom and hydraulic ram means construction wherein the portion of the boom on each side of the tractor is fabricated of plates to form substantially hollow boom portions, wherein the hollow boom portions are combined with hydraulic ram arrangements so that the hydraulic rams for raising and lowering the boom are completely protected by the boom and wherein the hydraulic rams are positioned substantially within the hollow of the boom portions when the bucket is positioned for digging at ground level.

It is another object of the present invention to provide a boom, linkage means and hydraulic ram means construction for a loader wherein the linkage means are operatively mounted in substantially the same vertical plane as the boom portions on each side of the tractor, and wherein the linkage means includes a lever which is pivotally carried within each boom portion intermediate the ends of the boom portions.

It is a further object of the present invention to provide a certain hollow boom fabrication for a loader wherein the hydraulic rams for raising and lowering the boom are mounted within the hollow boom portions with the cylinders of the hydraulic rams carried within the boom portions and with the rods of the hydraulic rams pivotally mounted to the tractor. 7

Other objects and features of the present invention will be apparent upon perusal of the following specification and drawings of which:

Figure l is a side elevational view of a loader con The present embodiment is the preferred embodiment H but it is to be understood that changes can be made in the present embodiment by one skilled in the art without departing from the spirit and scope of the present invention.

For a detailed description ofthe present invention reference is made to the drawing. The tractor or prime mover 10 which is of the four-wheel rubber-tired type well known in the art comprises a rearwardly disposed engine compartment 11, a forwardly disposed operator'scompartment 12 and wheels 13.

The bucket 14 for the loader may be of any suitable type well known in the art and is provided with pairs of flanges mounted on the rear side thereof for mounting the bucket to the boom and linkage means. The pairs of flanges comprise the four pairs of flanges 15 and the two pairs of flanges 16. The four pairs of flanges 15 are mounted transversely of the bucket 14 to the lower marginal edge of the rearward side of the bucket 14 with two pairs of flanges 15 disposed in spaced-apart relationship to each other as can be seen in Figures 1 and 3. The pairs of flanges 16 are mounted on the rear side of the bucket 14 transversely thereof and in a vertically spaced-relationship to the pairs of flanges 15.

The boom means 17 of the present invention, which is provided for carrying the bucket 14 from the tractor 10, comprises duplicate portions disposed on each side of the tractor 19. Since each portion of the boom means 17 is a duplicate of the other, a detailed description of one portion only need be made. One portion of the boom means 17 comprises two identically shaped boom arms 18. The two boom arms 18 are secured in a parallel spaced-apart relationship to each other by a number of plates designated with the numerals 19, 20 and 21. The plate 19 is secured between the upper longitudinal marginal edges of the boom arms 18 and intermediate the ends thereof in substantially the central section. The plates 20 and 21 are mounted between'the lower longitudinal marginal edges of the boom arms 18 in a spaced- 3 apart relationship to each .other and intermediate the ends ofthe boom arms 18. The relative positions of the plates 19, 20 and 21 to the other members will be described below. The rearward ends of the boom arms i I,P Y@ @ny.J11Qllntd between the outside wall of the tractpr ltlandjan t -s h aped member 22 immediately below the upper edge of the operators compartment 12. The L-shaped plate 22 which is provided in duplicate fpr each side of the tractor 10, is secured to the outside wall of the tractor with one leg thereof in a substantially horizontal plane and with the other leg thereof in a;su bstantially vertical plane spaced from the tractor 10. The bpom arms 18 ,are pivoted between the member 22 and the side walls of the tractor 10 by a pin 23. The forward end ,of each boom arm 18 is pivotally mounted between one pair of the pairs of flanges 15 by a pin 24. The shape .of the boom arms 18 may be likened to a modified S-shape. When the bucket 14 is in the dig position at ground level as shown in Figure l, the boom arms :18 ,are so shaped that from the pins 23 the boom arms 18 are .directedin a downwardly inclined direction toward the rear of the tractor 10. The boom arms 18 are then shaped to curve toward the forward end of the tractor 10 .and have a central section extending substantially horizontally. At the forward end of the tractor 10 and the horizontal central section, the boom arms 18 arecurved at a substantially right angle to the horizontal central section and in a generally downward direction. The extreme forward ends of the boom arms 18 are then curved in a forwardly downwardly inclined direction. The curve in the rearward section of the boom arms 18 is provided so that the boom arms 18 may in effect wrap around the tractor pivot pins of the linkage means when the boom arms 18 are raised to the high lift position as shown in Figure 2. Further, this curvature causes the central section to assume a substantially vertical position as shown in Figure 2 when the boom arms 18 are fully raised. This curvature of the central and rearward sections of the boom arms 18 permits a particular disposition of the rear pivot points of the boom means 17 and the linkage means which will be described below, and permits a raising and lowering of the boom means 17 between the position shown in Figure 1 and that shown in Figure 2 without at any time obstructing the view of the operator to either side of the tractor or offering a dangerous obstruction to the arms and shoulders of an operator within the operators compartment 12. The particular curvature of the forward sections of the boom arms 18 has a number of functions. Firstly, the bucket 14 is positioned substantially adjacent the forward end of the tractor 10. This is accomplished by the described curvature which directs the boom arms 18 immediately over the forward Wheel axles and then sharply toward the ground to bring the bucket 14 close to the forward end of the tractor 10. This is advantageous in that such an arrangement more evenly distributes the load to the tractor wheels, since the shorter the distance between the bucket and the tractor in any loader, the smaller moment a loaded bucket will place upon the front wheels of the tractor, and relatively, the greater will be the moment on the rear wheels, thus somewhat evenly distributing the load between all of the wheels of the tractor. Secondly, the curvature of the extreme forward end of the boom arms 18 permits the bucket 14 to be tipped back at ground level from the dig position, as shown in Figure 1, through an angle of at least 30. This arrangement is advantageous in that a load in the bucket may be broken away from any material which has been dug.

The boom means 17 described above uniquely cooperates with the specific raising and lowering means therefor to further provide certain efiiciencies in the function, structure, operation and results of the loader. To raise each pair of boom arms 18, a hydraulic ram 30 is provided. Each'hydraulic ram 30 comprises a cylinder portion 31 and a piston and rod assembly 32. The rod end of the cylinder portion 31 is provided with a collar 33. The collar 33 is pivotally mounted between the boom arms 18 by the pins 34. The location of the pins 34 pivotally positions the hydraulic ram 31 between the boom arms 18, as can be seen in Figure 3. The pins 34 are positioned between the plate 20 and the plate 19 substantially at the rearward end of the central section of the boom arms 18. The hydraulic ram 30 is of the type having ports at the outer end of the piston rod, having longitudinal passageways through the piston rod and the piston head so that hydraulic fluid may be admitted to and removed from the outer end of the piston rod to operate the hydraulic ram. Since this type of hydraulic ram is well known in the art, a detailed description and showing thereof is unnecessary. The outer end of the piston and rod assembly 32 is provided with a bearing 35 having ports therein for the connection of hydraulic lines thereto for interconnection with the longitudinal passageways within the piston rod. The bearing 35 is pivotally mounted within a'bracket 36 by means of a pin 37. The brackets 36 are secured to the outer wall of the tractor 10 substantially at the lower marginal edge thereof and adjacent to a vertical line at the rear end of the operators compartment 12. Hydraulic fluid lines 38 are connected between the bearing 35 of the tractor 10 and function as hydraulic fluid supply and return lines for the hydraulic ram 30. It can thus be seen that when hydraulic fluid is supplied to and returned from the hydraulic rams 30, the hydraulic rams 30 are extended and contracted to raise and lower the boom means 17. Figures 1 and 2, respectively, show substantially the extreme lower and upper limits of boom travel. When the hydraulic rams 30 are completely retracted, as shown in Figure l, the hydraulic rams 30 are positioned to lie substantially completely within the space defined by the boom arms 18 and the plates 19, 20 and 21. As the hydraulic rams 30 are extended to positions such as shown in Figure 2, the cylinder portions 31 of the hydraulic rams 30 are pivoted outwardly from the boom arms 18 and between the plates 20 and 21. The piston and rod assemblies 32 will project from the rearward curved portion of the boom arms 18. As can be seen from a comparison of Figures 1 and 2, the hydraulic rams 30 can operate to any degree between their extreme contracted positions and their extreme extended positions to efiiciently raise and lower the boom means 17. The telescoping effect shown by the operation of the hydraulic rams 30 and the boom means 17 functions to provide a compact structure for raising and lowering the bucket 14. The compactness is evident when consideration is given to the length and width of the various parts. Further, the boom means 17 func tions to protect the hydraulic rams 30, for as shown in Figure 1, in the completely retracted position of the hydraulic rams 30, hydraulic rams 30 are protected by the boom arms 18 and the plates 19. Additionally, in the raising and lowering of the boom means 17, it can be seen that the operator is not subjected to any dangerous scissors efiect between the boom arms 18 and the hydraulicrams 30. The assembly is at all times safe to an operator within the operators compartment 12.

The linkage means for pivoting and positioning the bucket relative to the boom means 17 comprises duplicate portions disposed on each side of the tractor 10. Each of the duplicate portions of the linkage means comprises a hydraulic ram 40, a lever 41 and a link 42. The head end of each of the hydraulic rams 40 is pivotally mountedv between the L-shaped member 22 and the side of the tractor 10 by a pin 43. A pin 43 is spaced forwardly and below pin 23 with the horizontal component of displacement substantially larger than the verarms 18 by a pin 44. The pin 44 is positioned substantially at the forward end of the central section of the boom arms 18. The upper end of the lever 41 and the rod end of the hydraulic ram 40 are pivotally interconnected by a pin 45. The lower end of the lever 41 and one end of the link 42 are pivotally interconnected by a pin 46. The other end of the link 42 is pivotally connected between the flanges 16 by a pin 47. Thus it can be seen that as the hydraulic rams 40 are extended and contracted respectively, the bucket 14 is caused to pivot rearwardly and forwardly with respect to the boom means 17. As shown in Figure 1, the hydraulic rams 40 are substantially, but not completely, extended. If the hydraulic rams 40, as shown in Figure l, are completely extended the levers 41 will be pivoted a certain small additional amount to move the links 42 to pivot the bucket 14 from the dig position at ground level to a break-out position at ground level. As shown in Figure 2, the hydraulic rams 49 are substantially completely retracted to cause the bucket 14 to assume the dump position relative to the boom means 17. It can be seen that as the hydraulic rams 40 are extended and contracted between the extremes thereof, the levers 41 will be pivoted about the pins 44 between the boom arms 18. In the extreme extended position of the hydraulic rams 40, the lower portion of the levers 41 will avoid the front axles of the tractor and the plates 21. In the extreme contracted position of the hydraulic rams 40, the upper portions of the levers 41 will avoid the forward edge of the plates 19. As the levers 41 are pivoted, the links 42 can freely move beneath the boom arms 18. This arrangement of the linkage means of the present invention provides maximum control over the pivoting of the bucket 14 relative to the boom means 17 to maintain a compact and efficient arrangement for the entire loader.

The horizontal displacement of the pins 23 and 43 and the vertical displacement of the pins 47 and 24 will cause a certain amount of automatic rearward tilt when the bucket 14 is raised from the dig position at ground level to a position before obstructing the forward vision of the tractor operator, and will cause a certain amount of forward tilting of the bucket 14 relative to the boom means 17 as the bucket is raised above the forward vision of the loader operator.

Hydraulic fluid pump, valve and conduit means (not shown) are provided for operation of the hydraulic rams 3t and 44 These means may be of any suitable type well known in the art.

Having described the invention, what is considered new and desired to be protected by Letters Patent is:

1. In a tractor leader, a boom for carrying a digging bucket, said boom comprising two identical portions, each of said portions comprising a pair of boom arms said boom arms positioned in a spaced apart relationship to each other, a plurality of plates, said plates secured in a spaced apart lfilfiiiOIlSZllP to each other between the longitudinal marginal edges of said boom arms, pin means for pivotally mounting one end of said boom arms on said tractor, a hydraulic ram for each pair of said boom arms for raising and lowering said boom, means pivotally mounting the cylinder portion of each of said hydraulic rams between said boom arms and said plates, second pin means for pivotally mounting the piston rods of said hydraulic rams to said tractor, said boorn arms shaped and said second pin means positioned so that said hydraulic rams are positioned substantially within the space defined by said boom arms and said plates when said boom is in the lowermost position, and means for mounting a digging bucket on the other ends of said boom arms.

2. In a tractor loader, a boom for carrying a digging bucket, said boom comprising two identical portions, each of said portions comprising a pair of boom arms, said boom arms positioned in a spaced-apart relationamps? I ship to each other, a plurality of plates, said plates secured in a spaced-apart relationship to each other between the longitudinal marginal edges of said boomand said plates, third pin means for pivotally mounting the piston rods of said hydraulic rams on said tractor at points adjacent to said boom arms when said boom is in the lowermost position whereby said hydraulic rarns are then positioned substantially within the space defined by said boom arms and said plates, and means for mounting a digging bucket on the other ends of said boom arms.

3. In a tractor loader, a boom for carrying a digging bucket, said boom comprising two identical portions, each of said portions comprising a pair ofboom arms, said boom arms positioned in a spaced-apart relationship to each other, a plurality of plates, said plates secured in a spaced-apart relationship to each other between the longitudinal marginal edges of said boom arms, pin means for pivotally mounting one end of said boom arms on the sides of said tractor immediately below the upper edge of the operators compartment thereof, said boom arms shaped to extend from said pin means in a curved direction rearwardly and then forwardly of said tractor when said boom is in the lowermost position and in a curved direction downwardly and then upwardly of said tractor and forwardly of said operators compartment when said boom is in the uppermost position, a hydraulic ram for each pair of said boom arms for raising and lowering said boom, means pivotally mounting the cylinder portion of each of said hydraulic rams between said boom arms and said plates, second pin means for pivotally mounting the piston rods of said hydraulic rams to said tractor so that said hydraulic rams are positioned substantially within the space defined by said boom arms and said plates when said boom is in the lowermost position and so that said cylinder portions of said hydraulic rams extend forwardly from the space defined by said boom arms and said plates when said boom is in the uppermost position, and means for mounting a digging bucket on the other ends of said boom arms.

4. In a tractor loader having a digging bucket and having linkage means pivotally connected between said tractor and said bucket for tilting said bucket to different positions, a boom for carrying said digging bucket, said boom comprising two identical portions, each of said portions comprising a pair of boom arms, said boom arms positioned in a spaced-apart relationship to each other, a plurality of plates, said plates secured in a spaced-apart relationship to each other between the longitudinal marginal edges of said boom arms, pin means for pivotally mounting one end of said boom arms on the sides of said tractor immediately below the upper edge of the operators compartment thereof and rearwardly and above the pivotal connection of said linkage means to said tractor, said boom arms shaped to extend from said pin means in a curved direction rearwardly and then forwardly of said tractor when said boom is in the lowermost position and in a curved direction downwardly and then upwardly of said tractor and forwardly of said operators compartment when said boom is in the uppermost position so that said boom arms are curved around the pivotal connection of said linkage means to said tractor, a hydraulic ram for each pair of said boom arms for raising and lowering said boom, means pivotally mounting the cylinder portion of each of said hydraulic rams between said boom arms and said plates, second pin means for pivotally mounting the piston rods of said hydraulic rams to said tractor so that said hydraulic rams are positioned substantially '7 within the space defined by said boom arms and said plates when said boom is in the lowermost position and so that said cylinder portions of said hydraulic rams extend forwardly from the space defined by said boom arms and said plates when said boom is in the uppermost position, and means for pivotally mounting said digging bucket on the other ends of said boom arms.

5. In a tractor loader, a boom for carrying a digging bucket, said boom comprising two identical portions, each of said portions comprising a pair of boom arms, said boom arms positioned in a spaced-apart relationship to each other, a plurality of plates, said plates secured in a spaced-apart relationship to each other between the longitudinal marginal edges of said boom arms, pin means for pivotally mounting one end of said boom arms on the sides of said tractor immediately below the upper edge of the operators compartment thereof, said boom arms shaped to extend from said pin means in a curved direction rearwardly and then forwardly of said tractor when said boom is in the lowermost position and in a curved direction downwardly and then upwardly of said tractor and forwardly of said operators compartment when said boom is in the uppermost position, a hydraulic ram for each pair of said boom arms for raising and lowering said boom, a collar secured about the cylinder portion of each of said hydraulic rams near the rod end thereof, second pin means pivotally mounting each of said collars between the boom arms of one of said pairs of boom arms and plates, third pin means for pivotally mounting the piston rods of said hydraulic rams to said tractor at points adjacent to said boom arms when said boom is in the lowermost position so that said hydraulic rams are positioned substantially within the space defined by said boom arms and said plates when said boom is in the lowermost position and so that said cylinder portions of said hydraulic rams extend forwardly from the space defined by said boom arms and said plates when said boom is in the uppermost position, and means for mounting a digging bucket on the other ends of said boom arms.

6. In a tractor loader, a boom for carrying a digging bucket, said boom comprising two identical portions, each of said portions comprising a pair of boom arms, said boom arms positioned in a spaced-apart relationship to each other, a plurality of plates, said plates secured in a spaced-apart relationship to each other between the longitudinal marginal edges of said boom arms, pin means for pivotally mounting one end of said boom arms on the sides of said tractor immediately below the upper edge of the operators compartment thereof, said boom arms shaped to extend from said pin means in a curved direction rearwardly and then forwardly to the forward end of said tractor at which point said boom arms extend substantially vertically downward with a forwardly curved section at the outer end thereof outwardly substantially to ground level when the boom is in the lowermost position and to extend from said pin means in a curved direction downwardly and then upwardly of said tractor and forwardly of said operators compartment when said boom .is in the uppermost position, a hydraulic ram for each pair of said boom arms for raising and lowering said boom, means pivotally mounting the cylinder portion of each of said hydraulic rams between said boom arms and said plates, second pin means for pivotally mounting the piston rods of said hydraulic rams to said tractor so that said hydraulic rams are positioned substantially within the space defined by said boom arms andsaid plates when said boom is in the lowermost position and so that said cylinder portions of said hydraulic rams extend forwardly from the space defined by said boom arms and said plates when said boom is in the uppermost position, and means for mounting a digging bucket on the outer ends of said boom arms so that said bucket is positioned substantially immediately forwardly ofsaid tractor when said boom is in the lowermost position and so that said bucket may be pivoted rearwardly a predetermined amount from the dig position at ground level.

7. In a tractor loader, a boom for carrying a digging bucket, said boom comprising two identical portions, each of said portions comprising a pair of boom arms, said boom arms positioned in a spaced-apart relationship to each other, a plurality of plates,'said plates secured in a spaced-apart relationship to each other between the longitudinal marginal edges of said boom arms, pin means for pivotally mounting one end of said boom arms on the sides of said tractor immediately below the upper edge of the operators compartment thereof, said boom arms shaped to form three contiguous sections, said three contiguous sections comprising a rearward section, a central section and a forward section, said rearward section formed in a curved direction rearwardly and then forwardly of said tractor when said boom is in the lowermost position and in a curved direction downwardly and then upwardly of said tractor and forwardly of said operators compartment when said boom is in the uppermost position, said central section formed to extend substantially horizontally from said rearward section to said forward section at the forward end of said tractor when said boom is in the lowermost position and in a substantially vertical direction and forwardly of the operators compartment when said boom is in the uppermost position, said forward section formed to extend substantially vertically downward from said central section with an outwardly curved portion at the outer end thereof when said boom is in the lowermost position and in a substantially horizontal direction with an upwardly curved portion when said boom, is in the uppermost position, a hydraulic ram for each pair of said boom arms for raising and lowering said boom, a collar secured about the cylinder portion of each of said hydraulic rams near the rod end thereof, second pin means pivotally mounting each of said collars between the boom arms of one of said pair of boom arms and said plates at the juncture of said rearward section and said central section, third pin means for pivotally mounting the piston rods of said hydraulic rams on said tractor at points adjacent to said rearward section of said boom arms when said boom is in the lowermost position so that said hydraulic rams are positioned substantially within the space defined by said central section of said boom arms and said plates when said boom is in the lowermost position and so that said cylinder portions of said hydraulic rams extend forwardly from the space defined by said central section of said boom arms and said plates when said boom is in the uppermost position, and means for mounting a digging bucket on the outer ends of said boom arms.

8. In a tractorloader having a digging bucket and having linkage means pivotally mounted to said tractor and to said bucket for tilting said bucket to different positions, a boom for carrying said digging bucket, said boom comprising two identical portions, each of said portions comprising a pair of boom arms, said boom arms positioned in a spaced-apart relationship to each other, a plurality of plates, said plates secured in a spaced-apart relationship to each other between the longitudinal marginal edges of said boom arms, pin means for pivotally mounting one end of said boom arms on the sides of said tractor immediately below the upper edge of the operators compartment thereof and rearwardly and above the pivotal connection of said linkage means to said tractor, said boom arms shaped to form three contiguous sections, said contiguous sections comprising a rearward section, a central section and a forward section, said rearward section formed in a curved direction rearwardly and then forwardly of said tractor when said boom is in the lowermost position and in a curved direction downwardly and then upwardly of said tractor and forwardly of said operators compartment when said boom is in the uppermostposition whereby said rearward section of said boom arms are curved around the pivotal connection of said linkage means to said tractor, said central section formed to extend substantially horizontally from said rearward section to said forward section at the forward end of said tractor when said boom is in the lowermost position and in a substantially vertical direction and forwardly of the operators compartment when said boom is in the uppermost position, said forward section formed to extend substantially vertically downward from said central section with an outwardly curved portion at the outer end thereof when said boom is in the lowermost position and in a substantially horizontal direction with an upwardly curved portion when said boom is in the uppermost position, a hydraulic rarn for each pair of said boom arms for raising and lowering said boom, means pivotally mounting the cylinder portion of each of said hydraulic rams between said boom arms and said plates, second pin means for pivotally mounting the piston rods of said hydraulic rams to said tractor so that said hydraulic rams are positioned substantially within the space defined by said central section of said boom arms and said plates when said boom is in the lowermost position and so that said cylinder portions of said hydraulic rams extend forwardly from the space defined by said central section of said boom arms and said plates when said boom is in the uppermost position, means for mounting said digging bucket on the outer ends of said boom arms.

References Cited in the file of this patent UNITED STATES PATENTS 

